For over 50 years the American population has been told to reduce total serum cholesterol in order to reduce risk of heart disease. For example the American Heart Association (AHA) website provides advice about acceptable total cholesterol levels: "Less than 200 mg/dL - Desirable level that puts you at lower risk for coronary heart disease. A cholesterol level of 200 mg/dL or higher raises your risk." The AHA also recommends dietary strategies for reducing total cholesterol: "It's not hard to whip up recipes that fit with the low-saturated-fat, low-cholesterol eating plan recommended by scientists to help you manage your blood cholesterol level and reduce your risk of heart disease and stroke." Dietary advice leans heavily on reduction of saturated fat to reduce cholesterol levels and therefore risk of heart disease. This idea that saturated fats are "artery clogging", called the "Diet Heart Hypothesis", first surfaced in the 1960's and remains a pervasive message to this day.
However the very foundation of this hypothesis was shaken to the core at the AHA annual conference in Chicago in 2010. Amid great excitement, the pharmaceutical giant Merck revealed results of a preliminary safety study for a drug that could usher in a new age for treatment and prevention of heart disease: a cholesterol raising drug! In the safety study lasting 18 months with 1,600 participants, total cholesterol was raised 20% by the drug anacetrapib without any side effects. An efficacy trail of 30,000 participants with several cardiovascular end-points is scheduled to begin in 2011 and end in 2015 to verify if cholesterol raising can reduce actual incidence of heart disease. But the search for cholesterol raising drugs is not new. Most of the cholesterol lowering statin drugs have reached the limits of their heart protective capabilities (and are near the end of their patent lives). For several years drug companies have been quietly searching for the next blockbuster that will be more effective than statins. One class of candidates is cholesterol raising drugs.
But haven't we been told over and over to lower our cholesterol, not increase it? Yes, but the cholesterol story has been repeatedly oversimplified. Total cholesterol is made up of 2 major components, good cholesterol (LDL) and bad cholesterol (HDL). So when your doctor tells you to lower your cholesterol, he really means lower your bad cholesterol – if you inadvertently lower your good cholesterol you could increase your risk of heart disease. The statin drugs selectively lower the bad cholesterol without lowering the good – and they work, reducing risk of heart attack by about 30%. The new class of drugs is designed to increase the good cholesterol, without increasing the bad. So in this case increasing cholesterol is a good thing. The scientific community is hoping that the upcoming Merck study will show a further reduction in risk of heart attack similar in magnitude to the statins – a real breakthrough.
Where does this leave the diet heart hypothesis, saturated fat and the simplified "lower your cholesterol" story? It leaves it in deep trouble. The advent of drugs that increase good cholesterol and thereby reduce risk of heart disease (yet to be proven), will force scientists to take another look at the effects of food ingredients on good cholesterol, not just the total and the bad. Applying this new approach could have a significant impact on national dietary recommendations that are designed to reduce risk of heart disease.
A large body of data showing the effect of food ingredients on both good and bad cholesterol has already been generated over the last 40 years. So far, the evaluation of this data has mostly focused on the bad cholesterol, while neglecting or even ignoring data for good cholesterol. But a review of the data for saturated fat gives a very unexpected result. The food component that increases good cholesterol the most is saturated fat! Yes, the same "artery clogging" saturated fat that has been demonized for decades. Although saturated fat still raises bad cholesterol, it appears that it raises good cholesterol by an equivalent amount and the effect of the bad cholesterol is mostly cancelled out. In this scenario saturated fat is expected to have little or no effect on risk of heart disease.
But good and bad cholesterol are components of blood, and not actual disease. What about direct evidence for the effect of saturated fat on incidence of heart disease? Early in 2010 a large human study measuring the link between intake of food components and heart disease was published. The study included over 340,000 people spanning 23 years. Here is what the authors said about saturated fat: "…there is no significant evidence for concluding that dietary saturated fat is associated with an increased risk of CHD or CVD." Or in plain English - saturated fats have no effect on heart disease. Although this statement appears to fly in the face of everything we have been taught for decades, it corresponds exactly with powerful ability of saturated fat to increase good cholesterol. Neglect of the positive effect of saturated fat on good cholesterol has made it look worse that it really is.
A convincing body of evidence already exists that saturated fat is not as bad as once thought. Nevertheless public policy continues to demand further big reductions in saturated fat intake. The 2010 Dietary Guidelines Advisory Committee (DGAC) recommended reducing saturates by 5% of the diet. If this huge reduction was ever implemented, the US dairy and meat industries - the main dietary source of saturated fat - would be severely damaged, and all for nothing. Isn't it time to abandon the failed Diet Heart Hypothesis and focus our resources on issues that really make a difference to public health?